Silica-based glass, such as soda-lime-silica glass, is prevalent in the manufacture of glass containers and other articles. Molten glass used to make such articles is conventionally prepared by reacting and melting a batch of glass-forming materials in a refractory lined, continuously operated glass furnace, tank, or pot. The batch of glass-forming materials is typically introduced into the furnace by being deposited onto a pool of molten glass already in the furnace and is gradually melted into the pool by the continuous application of heat. After the batch has been melted, refined, and homogenized within the furnace, the resulting molten glass is typically directed to one or more forehearths where it is thermally conditioned by being cooled to a suitable temperature for forming. A feeder located at a downstream end of the one or more forehearths may be used to measure out predetermined amounts of molten glass known as “gobs.” The gobs may then be formed into individual glass articles by a glass forming machine. U.S. patents that illustrate glass manufacturing processes of this type include U.S. Pat. Nos. 2,593,197; 2,955,384; 2,975,224; and 3,057,175.
Commercial-scale glass furnaces are typically designed to produce several hundred tons of glass per day. As such, these furnaces typically hold, on a continuous basis, relatively large volumes of molten glass having depths of between two and four feet. The thermal and structural stability of these glass furnaces is provided by lining the furnaces with relatively thick layers or bricks of refractory material. In order to prevent damage to the refractory linings of such furnaces, it is generally believed to be desirable to operate the furnaces on a continuous basis and to constantly maintain the glass within the furnace in a flowable molten state, as doing so helps avoid temperature variations and/or fluctuations in the furnaces, which helps reduce thermal stresses within the refractory linings of the furnaces. However, the continuous operation of such furnaces may result in a production rate of glass articles that is greater than the actual demand for new glass articles. In addition, even if the production of glass articles is stopped, for example, during a holiday period, a continuous supply of heat must still be applied to the glass within the furnace during the entire stoppage period in order to continuously maintain the glass in a molten state.
A general object of the present disclosure, in accordance with one aspect of the disclosure, is to provide a process for making glass and glass articles that can be operated in a more energy efficient and economical manner than conventional glass manufacturing processes.
The present disclosure embodies a number of aspects that can be implemented separately from or in combination with each other.
A process for making glass in accordance with one aspect of the disclosure includes: (a) compacting glass batch materials into a continuous sheet having a thickness of less than three centimeters; (b) flowing the sheet down a downward sloping surface; and (c) selectively and locally heating one or more portions of the sheet to melt the sheet as the sheet flows down the downward sloping surface. The one or more portions of the sheet may be selectively and locally heated in step (c) using electric heaters, induction heaters, fuel-fired heaters, microwave generators, or a combination thereof.
In accordance with another aspect of the disclosure, there is provided a process for making glass gobs on demand that includes: (a) providing a sheet of molten glass having a thickness in the range of two centimeters to seven centimeters in a staging section; (b) holding the sheet of molten glass in the staging section when there is no demand for glass articles; and (c) flowing a portion of the sheet into a gob forming section when there is a demand for production of glass articles. The sheet of molten glass may be allowed to solidify within the staging section, the gob forming section, or both during a non-production period, and may be re-melted when production resumes. A discrete gob of molten glass having a predetermined length, width, and thickness may be formed by cutting the portion of the sheet that has been flowed into the gob forming section from a remaining portion of the sheet.
In accordance with yet another aspect of the disclosure, there is provided an apparatus for making glass gobs on demand that includes: a hopper to distribute glass batch materials over a surface as a continuous layer; a compactor to compact the layer into a sheet having a thickness of less than ten centimeters; a melting and refining section having inlet and outlet openings and a downward sloping surface extending therebetween; a conveyor to carry the sheet from the compactor to the melting and refining section; a heater to selectively and locally heat the sheet within the melting and refining section as the sheet flows down the downward sloping surface; a staging section positioned to receive the sheet as the sheet flows out the outlet opening of the melting and refining section; and a gob forming section positioned to receive an end portion of the sheet from the staging section and to cut the end portion of the sheet from a remaining portion of the sheet to form a discrete gob of molten glass having a predetermined length, width, and thickness.